Synthesis of phthalocyanines with two carboxylic acid groups and their utilization in solar cells based on nano-structured TiO2

A method for anchoring unsym. phthalocyaninato-metal complexes (metal ion: zinc and ruthenium) is described. The synthesis and characterization of these complexes, ZnL and Ru(4-picoline)2L (H2L = 2,3-bis(carboxyphenoxy)-9,10,16,17,23,24-hexakis(pentoxy)phthalocyanine) are presented. In case of the zinc complex, the obtained product is an aggregate, while only the monomer was obtained in the case of the ruthenium deriv. Both complexes could be attached onto the TiO2 surface by using the reported method. Both dyes are expected to form monolayers with dye mols. standing on the surface of nano-structured TiO2, forming higher-order aggregates with the zinc but not with the ruthenium complex. A highest monochromatic incident photo-to-current conversion efficiency (IPCE) of 1.6% at 690 nm was obtained for a solar cell based on the Pc-Zn sensitized nano-structured TiO2 electrode, while an IPCE of 23% at 630 nm was obtained for the Pc-Ru sensitized electrode. Overall conversion efficiencies (η) at a simulated AM 1.5 (100 W m-2) of 0.03% and 0.40% for the zinc and ruthenium complexes were achieved, resp. The difference in efficiencies could be due to the formation of face-to-face aggregation in the former case. The ruthenium complex, with two axial methylpyridine ligands, does not form aggregates in soln. nor on the surface of TiO2, making it possible for further construction of supramol. systems with such types of phthalocyanine.